Study On The Recovery Of Rare Earth Elements Pr And Nd From Molten Salt Electrolytic Slag

The rare earth smelting industry of our country often produces rare earth by means of molten salt electrolysis under the system of REF₃-LiF₃-RE₂O₃.When preparing rare earth by means of molten salt electrolysis,a large number of rare earth molten salt electrolytic slag(rare earth fluoride or rare earth fluoride)will be produced.Its rare earth content is high,its composition is complex,and it is difficult to recover and treat.It is of great significance to realize the recycling of rare earth solid waste.Aiming at the problem of difficult separation and extraction of rare earth from rare earth molten salt electrolytic residue,this paper puts forward the process research of high efficient recovery of residual rare earth from ore phase reconstruction by making full use of physical and chemical characteristics of rare earth and its impurities.(1)In this paper,the rare earth molten salt slag raw material for X-ray fluorescence spectroscopy and X-ray diffraction(XRD)analysis of rare earth elements in rare earth molten salt slag is analyzed and the existence of impurities,proven rare-earth molten salt slag mainly exists in the form of fluoride,fluoride oxide,the total rare earth content is 51.2%,Nd₂O₃ content is 76.69%,Pr₆O₁₁content is 22.96%,more than 83%of rare earth fluoride accounted,also contain a small amount of Al,Fe and Ca impurities.(2)Respectively from sodium carbonate,sodium hydroxide,sodium silicate,three kinds of roasting convert agent,through the round of salt or alkali roasting,realization of rare earth molten salt slag phase reconstruction,control variable method is used for experiments,to explore the effects of rare earth leaching ratio,select the best roasting conditions(calcination time,calcination temperature,salt slag mass ratio),washing conditions(washing time,temperature and water washing times)and acid leaching conditions(Hydrochloric acid concentration,acid leaching time,temperature,solid-liquid ratio,stirring speed).The leaching rate of sodium carbonate roasting method is higher than 98%,sodium silicate roasting method is 96%,sodium hydroxide roasting method is only about 95%.Finally,the sodium carbonate method is the best process.(3)Using HSC Chemistry reaction to sodium carbonate roasting reaction heat calculation software and differential thermal analysis,shows that when the reaction temperature is 700?,?G<0,reactions can occur spontaneously,and at 600?or so intense reaction,therefore,can be set for sodium carbonate roasting temperature in600??700?is the best.Potential-p H was also analyzed in this paper,which can reflect the existence forms of various ions and compounds in the system of F-Cl-Na-Nd-H₂O at 80?.(4)By expanding the experiment,the experimental conditions were as follows:roasting temperature 700?,roasting time 1.5h,mass ratio of salt-slag 0.6:1,washing time 1h,washing temperature 50?,washing times twice,acid leaching time 2h,hydrochloric acid leaching concentration 3mol·L^-1,acid leaching temperature 80?,liquid-solid ratio 10:1,stirring speed 400r·min^-1.The leaching rate of rare earth was98.46%.The results showed that the expanded experiment further improved the leaching rate of rare earth,and optimized the process of"reducing alkali/salt roasting-water fluorine-acid leaching of rare earth",which has guiding significance for practical production and application.